Understanding Active Directory Objects
The Active Directory database is made up of units called objects. Each object represents a single unique database entry.
Names and Identifiers of Objects
Objects are uniquely identified within your database in the following ways:
GUIDs and SIDs
Globally unique identifiers are security identification numbers placed on applications by Active Directory. These numbers are guaranteed to be unique, but the number generated is very large, so the odds are very low that two applications will end up with the same GUID.
Security identifiers are security identification numbers placed on objects ...